300tid tappet style noise, but only under load?

A noise that runs at about the frequency of one valve.

But the confusing thing is that it only happens under load. Any load, not just hard load.

So I can be driving up a gentle incline, and the knocking is there, but, as I crest the (gently) hill, and it comes off load (I'm not talking freewheeling down hill, just as it starts to slope down but I've still got my foot in the same place) the ticking / knocking stops.

Put my foot down just gently again, and it's back. I can literally turn it on and off by gently taking it on and off load.


It's quite loud though and I'm sure it's getting worse.


I'm trying to work out what it could be. Things like the vac pump, lift pump, and tappets would not change like this, would they?

The frequency is tied to the engine, rather than road speed, so that would rule out drive train.


Engine starts nicely. I've not spotted any indication of head gasket issues.



Id say tappets but I can't see how they would only make noise under load, and Google doesn't seem to tell me they would either.


Any ideas?

Injector knock possibly.

I fitted recon injectors in 2016, and then the the vehicle was laid up until 2 years ago when I did the bulkhead.

So they've had time, but not miles on them, if that makes sense?


It's so hard to pinpoint a fault that only makes noise when under load. I mean how do you start poking about with your ear in the engine bay when driving down the road!

Stick contact mics on various bits I guess. Not that I'm going to do that.

Thank you.

Check the injector pump timing if it is too advanced that will give you a knock